EP2350475B1 - Fastening element for screw connections and use thereof - Google Patents

Description

Field of the invention

The invention relates to a mechanical screw lock in the form of a securing element for screw connections as an intermediate layer between the screw head and the support material and / or between the nut and the support material and the use of such a securing element for heavily loaded, permanent and detachable screw connections.

Background of the invention

Screw connections are used in all areas of mechanical, plant and automotive engineering to achieve positive connections. Especially with dynamic loading of the screw connections, many of the conventional screw connections do not ensure sufficient safety against an automatic release of the screw connections. One is therefore anxious. Provide measures to secure screw to prevent at high and especially dynamic loads an automatic release of the screw.

State of the art

There are several mechanical threadlockers available commercially. Examples of such screw locks are the rib screw, the locking tooth screw, the NordLock disc pair, the Teckentrup disc and the Schnorr disc.

The example in the DE 25 56 985 A1 described rib screw (or the rib nut) has a profiling on the underside of the screw head. Due to the elastic ribs, the securing effect occurs in the slightly plastic area of the supports (roller effect). This does not use a separate lock washer.

The NordLock screw lock (anti-rotation lock) uses a pair of wedge lock washers. The disks have on the outside radial ribs and on the inside wedge surfaces, whose slope always larger than that Thread pitch is. The paired glued discs are placed under the screw head and / or the nut. Due to the radial ribs, a tight fit occurs during tightening. The disc pair is now firmly in place and movements are only possible between the wedge surfaces. Already at the slightest rotation in the release direction is due to the wedge effect an increase in the clamping force and the screw secures itself thus. A mounting element for a NordLock wedge pair is for example in the WO 02/31368 A1 described.

The Schnorr disc is a resilient disc between the screw head and the workpiece, which is toothed at the top and bottom.

The Teckentrup disc secures positively and positively against loosening and loosening of screw connections. The adhesion of the Teckentrup disc is caused by spring force. The positive locking reaches the Teckentrup disc by a specific surface embossing.

Some of these threadlockers have proven to be unusable, such as the Teckentrup and Schnorr discs (see comparative examples). The Teckentrup and Schnorr discs do not offer a securing effect against loosening under transverse load. The NordLock disk pair has the disadvantage that under dynamic loading of the screw connections, a loss of prestressing force occurs due to settling and / or relaxation, in particular in the case of high-strength bolts of strength classes 10.9 and 12.9 (see comparative examples).

The ratchet screw is as the rib screw a head-locking system, for which no separate fuse element is needed. Although the ratchet screw shows a good securing effect, but is disadvantageous in that the teeth penetrate into the counter layers, so the surfaces of the support materials, and that it thus comes to a relatively large violation of the surfaces of the support materials. The ribs of the NordLock discs also penetrate into the antagonists.

A large violation of the surface of the support materials also has a very negative effect on the re-screwability. The surface roughness is greatly changed, which increases the Unterkopfreibung uncontrolled and thus changed the preload force.

The rib screw shows a good securing effect (see Comparative Example 1).

When using head locking locking screws (steel screws) in light metal or aluminum constructions, which experience operating temperatures of 110 ° C and more, the steel screws are loaded beyond the yield point. After re-cooling to room temperature increased Vorspannkraftsetzverluste occur.

Another disadvantage of the head-locking systems is that the head-locking screws and nuts must be cleared in the restricted areas in case of multiple use.

Furthermore, there are thread locking systems such as Spira-Lock (locking thread with a special design of the thread profile). A disadvantage of these systems is that dry lubricated screws must be used, since the friction values in the unlubricated state over μ ges = 0.25, while the VDI 2230 provides for the calculation of a coefficient of friction μ ges = 0.12.

Another possibility for securing screws is the bonding by means of a liquid plastic. For this, however, a high degree of purification is required, which leads to an increased cost.

In the DE 40 38 557 C2 is described a locking washer for screw that consists of a paper, plastic or metal foil in a thickness of 0.1 to 0.3 mm with stuck on the top and bottom hard particles. The hard particles are preferably oxide ceramic round particles having a size of 50 to 150 μm.

A lock washer according to DE 40 38 557 C2 has not proven itself in practice. The round particles used here favor the sliding of the separating surfaces to each other, which is disadvantageous in terms of securing effect. The use of particles of a size of 50 to 150 microns leads to a gap that may adversely affect the planarity of the substrates and the planarity of the contact surfaces. Due to the low shear strength of the adhesive, there is also the problem that the particles do not remain in their original position during the screwing process and the resulting relative movement between particles and surfaces, which results in uncontrolled, inhomogeneous coating of the surface with particles. In addition to the unsuitable spherical particle shape, this leads to a poor overall securing effect.

EP 0 961 038 A1 (KEMPTEN ELEKTROSCHMELZ GMBH [DE], WACKER GMBH [DE]) describes a connecting element for the friction-increasing connection of workpieces to be joined, which consists of a thin elastic film, the film carries on its surface particles of defined size. These particles consist of a material with a compressive and shear strength which are greater than those of the workpieces to be joined.

EP 1 300 485 A1 (WACKER GMBH [DE]) describes a force-transmitting surface layer coated with friction-enhancing particles in a matrix. This matrix comprises an upper and a lower layer, wherein the lower layer is a metallic binder phase which is usual for a friction-increasing fixation, and the upper layer is a further metallic binder phase with a diameter dependent on the diameter of the particles.

Object of the invention

The invention is therefore based on the object to provide a screw lock available, which is at least equivalent or superior in terms of securing effect to the known prior art threadlockers, but which avoids the disadvantages of the prior art, in particular not a relatively large penetration the screw lock in the surface of the support material and thus does not lead to a relatively large violation of the surface of the support material, and which can be used for highly loaded, permanent, re-releasable and re-screwed screw.

Summary of the invention

The above object is achieved by a securing element for screw according to claim 1 and its use according to claim 10. Advantageous and particularly expedient embodiments of the subject of the application are specified in the dependent claims.

The invention thus relates to a securing element for screw connections as an intermediate layer between the screw head and the support material and / or between the nut and the support material, wherein the base body of the element consists of a metallic material, on the upper and lower side of hard material particles are fixed, which is characterized in that the hard material particles are fixed by means of a metallic binding phase, wherein the thickness of the metallic binding phase maximally about 60% of the mean Diameter of the hard material particles is so that the hard material particles protrude from the metallic binder phase, and wherein the hard material particles have a maximum diameter of 100 microns and a mean particle size D ₅₀ in the range of 8 - 35 microns.

The invention also relates to the use of a securing element according to the invention for highly loaded, permanent and re-releasable screw, wherein the securing element is used as an intermediate position between the screw head and the support material and / or between the nut and the support material.

A significant advantage of the securing element according to the invention is that it comes with the screw to a relatively low penetration into the surface of the support materials and thus to only a relatively minor violation of the surface of the support materials.

For conventional security systems with fluted surfaces in the screw head underside such as the locking screw or in lock washers such as the NordLock disc pair, the injury depth is in the range of about 100 to 200 microns, while using the fuse element of the invention, for example when using a hard material grain size with an average particle size of 10 microns, only about 4 - 6 microns corresponding to the free grain supernatant.

In the case of opening and closing a screw connection secured according to the invention, the mating surfaces are only slightly damaged, so that the mating surfaces need not be cleared, cleaned or mechanically reworked before the connection is closed again.

With the securing element according to the invention, therefore, a re-screwing is possible without expensive cleaning and processing measures are required, ie the screw assemblies do not need to be revised before re-screwing. Preferably, however, a new securing element is used for a re-screwing. The fuse element of the present invention can be used in all materials, including all hardened materials, unlike some of the commercially available safety systems such as the head locking systems and the NordLock disk pair that can only be used in uncured materials are. Also in light metal structures, for example in aluminum structures, the fuse element according to the invention can be used.

If a thin coated film with a thickness of 0.1 mm is used as the securing element according to the invention, this results in the additional advantage of a considerable weight saving compared to standard securing elements, for example, in a standard M6 screw with a standard locking washer of 1.6 mm thickness is already about 94%, as well as the advantage of a smaller installation space.

Detailed description of the invention

The main body of the securing element according to the invention consists of a metallic material, preferably steel and more preferably spring steel. It can be used a commercially available unalloyed spring steel strip. Such spring-elastic steels preferably have a tensile strength in the range of 350-1850 N / mm ² , more preferably 800-1600 N / mm ² . But it can also be used other, especially softer steels. Depending on the application, acid- and / or temperature-resistant steels are used.

The thickness of the securing element depends both on the application and on the screw size and is preferably ≦ 2 mm, more preferably ≦ 0.2 mm, and particularly preferably 0.1-0.2 mm. Thin films of a thickness of 0.1 to 0.2 mm are preferably used when weight saving and limited space or packing density play a role. Thicker elements are used, for example, in larger glands and multiple screw connections or flanges, in which no individual elements should be used. The thickness of the elements can be selected according to DIN 125 depending on the screw diameter.

The elements can be produced by punching, lasering or eroding.

The hard materials used are preferably materials which under the respective conditions of use neither with the materials of the screw connections still chemically react with ambient media. Preferred examples of hard materials are carbides such as SiC, WC and B ₄ C, nitrides such as Si ₃ N ₄ and cubic BN, borides or SiO ₂ or Al ₂ O ₃ or diamond. Particular preference is given to using diamond, B ₄ C or SiC.

The size of the hard particles should be chosen so that the damage to the support materials does not reach an unacceptable level due to the particles being pressed in. A particle size with a maximum diameter of 0.1 mm generally meets this requirement.

Particular preference is given to using hard particles having a maximum diameter of 35 μm. The hard particles have an average particle size D ₅₀ in the range of 8 to 35 .mu.m, preferably from 10 to 25 .mu.m. The determination of the grain size is carried out in a known manner by means of laser diffraction, for example with a device from CILAS (CILAS 1064), to solid dispersions.

In cases in which existing corrosion protection layers must be penetrated, it may be useful to use hard particles of a mean size of more than 30 microns. Typical corrosion protection measures are phosphating and cathodic dip paint. Phosphatizations usually have layer thicknesses of up to 15 μm, KTL coatings of up to 25 μm. For phosphating, therefore, the use of hard particles with an average diameter of 35 microns may be useful.

The number of hard particles per unit area of the contact surfaces of the support materials is preferably to be selected so that when tightening the screws, a depression of the particles is ensured in the mating surface. For this purpose, at least 5% of the contact surface of the fuse element should be covered with hard particles, an occupancy greater than 30% brings no further benefits.

The securing elements according to the invention in the form of perforated elements are coated with a metallic layer with embedded hard material particles. The coating preferably takes place by means of electroplating processes. The coating is preferably carried out after the production of the hole elements, but it is also possible to perform a coil coating and then separate the individual elements from the belt, for example by punching or lasering.

The metallic layer serves as a binding phase for the hard material particles. Particularly preferably, the coatings can be produced by means of an electroless (= chemical) nickel plating. The applied chemical nickel layers can be cured by a heat treatment to about 400 ° C, whereby the adhesion to the element material is improved and the inherent strength of the layer is increased.

In a preferred embodiment, the strength of the metallic binder phase is at least as high as the strength of the support and screw material. But it is also possible that the strength of the binder phase is less than the strength of the support and screw material.

The thickness of the metallic binder phase should be less than the average particle size of the hard particles, so that they protrude from the coating and can intervene in the surface of the support materials. The thickness of the metallic binder phase is at most about 60% of the mean diameter of the hard material particles. The layer thickness is thus to be selected as a function of the particle size of the hard particles. For example, the layer thickness should be about 6 microns with an average particle size of the hard particles of 10 microns.

The coated safety elements are resistant to acids and alkalis and temperature resistant. When using diamond as a hard material particles, temperature applications up to about 500 ° C, for carbides up to higher temperatures of about 800 ° C are possible.

The securing element according to the invention can be designed as a single-hole or multi-hole securing element. In the simplest and preferred embodiment, the securing element according to the invention is a securing disk, in particular a single-hole or multi-hole disk. However, the securing element can also have any regular or irregular outer contours, for example, to adapt to the contours of the support material of the screw. This applies to both single and multiple security elements.

The securing element according to the invention can be used in particular for highly loaded, permanent screwed, which must be releasable and re-screwed again. It can be used for fittings that need to be usable again without costly cleaning or clearing the Verschraubungsflächen.

Usually, one securing element is used per screw connection, which is placed under the screw head and / or the nut and screwed. However, it is also possible to use a single fuse element for multiple screws, in which a connection is made by several screw connections side by side, instead of individual securing elements for each of the screw together for all screws together. This securing element can be, for example, a circular disc in which a plurality of circular openings are present for the individual screws, but also other outer contours are possible. Such Mehrfachsicherungsscheibe offers advantages for the installation of such a compound, since then not individual lock washers must be placed individually and screwed.

Examples and Comparative Examples

The following examples and comparative examples serve to further illustrate the invention.

example 1 Production of a security element according to the invention Perforated disk D _a = 20 mm D _i = 10.3 mm h = 2 mm

To produce a securing element according to the invention, initially annular disks in the dimensions d20 / 10.3 * 2.0 mm are punched from uncoated 2.0 mm thick sheet steel C 75 S + QT. This sheet has a strength of 1412-1449 N / mm ² .

The prefabricated discs are placed on suitable holders and pre-treated by degreasing, pickling and activating according to the general rules of electroplating.

Then, the product carrier with the disks is immersed in a chemical nickel bath in which diamond powder with 20 μm average particle diameter is dispersed. The amount of dispersed diamond powder is chosen so that the desired surface coverage of diamond particles is achieved at the conditions prevailing in the coating bath (bath movement, deposition rate). In the present case, an area occupancy of 19.5 ± 1.5% was determined. The thickness of the deposited metal layer was set at 10 microns so that the free grain supernatant corresponds to about 50% of the grain diameter. In order to achieve a very uniform grain supernatant, it is advantageous to fix the diamond particles in a first coating step on the wafer surface, wherein the layer thickness is <3 microns. In a second coating step, the final layer thickness is set in a solids-free nickel bath. Under normal process conditions, the total immersion time in the coating baths is about 30 minutes.

The product carrier with the now coated discs is removed from the coating and cleaned in an ultrasonic bath to remove only loosely adhering diamond particles.

The cleaned slices are removed from the product carrier and subjected to a heat treatment of 2 hours at 350 ° C. This treatment improves the adhesion of the chemical nickel layer to the steel foil as well as the location of the particles in the layer itself. Depending on the substrate, heat treatment at reduced temperatures may also be advantageous.

Example 2 and Comparative Examples 1 to 4

To investigate the securing effect, a vibration test according to DIN 65151 with 12.5 Hz of dynamically changing lateral force load was carried out on a junk test rig of the Junker type. The preload force curve was measured and registered as a function of the load changes (time). In each case 1000 load changes were carried out. For the tests, black M10 screws according to DIN EN ISO 4017 were used in strength class 10.9 according to ISO 898-1. The clamping length was 1.5 mm. The screws were tightened quickly and evenly with a torque wrench. The preload force was 40 kN.

The assessment of the securing effect is based on the preload force drop over the trial period. If the preload force at the end of the experiment is still 80% of the original preload force and more, then the securing effect of a Losdrehsicherung is given. If the prestressing force at the end of the test is below 80%, but still amounts to at least 20%, then the effect of a captive safety device is still present. If the preload force at the end of the test is below 20%, the securing element is unusable.

The following materials were used for the tests: a structural steel of medium hardness (hardness 163 HV5, material designation S355J2G3 or St 52-3), a casting material (EN-GJL-250), a case hardening steel (hardness 210 HV5, material designation 16MnCr5) and an aluminum material (AlMgSi1). The surface roughness of the cladding materials was R _a = 1 μm, for the cladding materials S355J2G3 and EN-GJL-250 additional tests were carried out with R _a = 2.5 μm.

As securing elements for the tests, a locking washer according to the invention were used according to Example 1 and other commercial threadlockers (lock washers NordLock, Teckentrup and Schnorr and the ribscrew with the profiling on the underside of the screw head).

The result of the tests after 1000 load changes is shown in Tables 1 and 2.

Table 1 shows for the experiments carried out how high the preload force was after 1000 load changes, based on the preload force at the beginning of the experiments. This value should be at least 80%, so that a good anti-rotation effect is given. In the experiments with the Schnorr disc and the Teckentrup disc, the preload force had already dropped to zero after less than 1000 load changes, in the table in these cases is indicated in each case in square brackets after how many load changes, the preload force had dropped to zero.

Table 2 shows the evaluation of the tests carried out with regard to the securing effect.

From Table 2 it is apparent that the securing element according to the invention and the commercial ribbed screw very well meet the requirements for the securing effect of a Losdrehsicherung. In contrast, the "NordLock" safety device is already somewhat worse, since the prestressing force in the tested bearing materials drops significantly during the test. The Schnorr disc and the Teckentrup disc both proved useless. The drop in the preload force is in the tests with the lock washer according to the invention according to Example 1 partially smaller than in the experiments with the rib screw.

After the tests, the depth of penetration of the aluminum support material was measured by means of confocal laser scanning microscopy. The mean punctual injury depth is 10 microns for the experiments carried out with Example 1, in Comparative Example 1 (rib screw), it is flat 140 microns. <u> Table 1 </ u>: Pretension force after 1000 load cycles, relative to preload force at the beginning of the experiments S355J2G3 (St 52-3) EN-GJL-250 16MnCr5 AlMgSi1 R _a = 1 R _a = 2.5 R _a = 1 R _a = 2.5 R _a = 1 R _a = 1 example 1 88% 86% 93% 91% 87% 90% Comparative Example 1 (ribbed screw) 87% 88% 87% 87% 87% 88% Comparative Example 2 (Nord-Lock) 77% 78% 81% 81% 79% 76% Comparative Example 3 (Schnorr disc) 0% [250] 0% [300] 0% [300] 0% [300] 0% [300] 0% [220] Comparative Example 4 (Teckentrup) 0% [600] 0% [380] 0% [400] 0% [350] 0% [400] 0% [400] S355J2G3 (St 52-3) EN-GJL-250 16MnCr5 AlMgSi1 example 1 Very good anti-rotation lock Very good anti-rotation lock Very good anti-rotation lock Very good anti-rotation lock Comparative Example 1 (ribbed screw) Very good anti-rotation lock Very good anti-rotation lock Very good anti-rotation lock Very good anti-rotation lock Comparative Example 2 (Nord-Lock) Satisfactory (captive at the border to the Losdrehsicherung) Good (anti-rotation lock, but lower preload than above) Satisfactory (captive at the border to the Losdrehsicherung) Satisfactory (captive at the border to the Losdrehsicherung) Comparative Example 3 (Schnorr disc) unusable unusable unusable unusable Comparative Example 4 (Teckentrup) unusable unusable unusable unusable

Claims (10)

1. A securing element for screw connections as an interlayer between the screw head and supporting material and/or between the nut and supporting material, the basic body of the element consisting of a metallic material, to the top side and underside of which hard material particles are fixed, characterized in that the hard material particles are fixed by means of a metallic binding phase, the thickness of the metallic binding phase amounts to a maximum of about 60% of the mean diameter of the hard material particles, so that the hard material particles project out of the metallic binding phase, and wherein the hard material particles have a maximum diameter of 100 µm and a mean grain size D₅₀ in the range of from 8 to 35 µm.
2. The securing element as claimed in claim 1, characterized in that the metallic material of the securing element is steel, preferably spring steel, further preferably spring steel with a tensile strength of 350-1850 N/mm².
3. The securing element as claimed in claim 1 and/or 2, characterized in that the securing element has a thickness of ≤ 2 mm, preferably ≤ 0.2 mm, further preferably 0.1-0.2 mm.
4. The securing element as claimed in at least one of the preceding claims, characterized in that the hard material particles are selected from the group consisting of carbides, nitrides, borides, diamond, SiO₂ and Al₂O₃, preferably from the group consisting of diamond, silicon carbide and boron carbide.
5. The securing element as claimed in at least one of the preceding claims, characterized in that the hard material particles have a maximum diameter of 35 µm, and a mean grain size D₅₀ in the range of 10 to 25 µm.
6. The securing element as claimed in at least one of the preceding claims, characterized in that 5 to 30% of the contact surface of the securing element is covered with hard material particles.
7. The securing element as claimed in at least one of the preceding claims, characterized in that the metallic binding phase is a chemical nickel layer generated by electroplating.
8. The securing element as claimed in at least one of the preceding claims, characterized in that it is a single-hole securing element, preferably a single-hole washer.
9. The securing element as claimed in at least one of claims 1-7, characterized in that it is a multiple-hole securing element, preferably a multiple-hole washer.
10. The use of a securing element as claimed in at least one of claims 1 to 9 for highly loaded, permanent and rereleasable screw connections, the securing element being used as an interlayer between the screw head and supporting material and/or between the nut and supporting material.